What is an electrical order (or mechanical order)?

Definition

An electrical order ke is the ratio between an excitation frequency f with the fundamental electrical frequency fs:

k_{e}=f/f_{s}

Similarly, the mechanical order km is the ratio between an excitation frequency f with the rotational mechanical frequency fR:

k_{m}=f/f_{R}

For synchronous machines we therefore have

k_{m}=p k_{e}

where p is the pole pair number.

Application to e-NVH

The frequency of electromagnetically-excited acoustic noise frequency is the same as the exciting force. Besides, most of Maxwell force harmonics are proportional to speed in synchronous machines. A magnetic excitation or acoustic line can therefore be characterized by its electrical or mechanical order, rather than being characterized by its frequency.

As an example, a 48 stator slot 8-pole permanent synchronous machine has radial force harmonics of wavenumber r=0 occuring at LCM(Zs,2p)fR=12fs. These pulsating forces have an electrical order 12, or a mechanical order 48. The mechanical order is sometimes noted as H48 like "mechanical harmonic of order 48".

In asynchronous machines, the concept of orders still holds in no-load conditions (null slip). However in load conditions some of the magnetic excitations are proportional to the rotational frequency, and some others are not.

Application to MANATEE

MANATEE software post processing allow to plot all quantities (permeance, flux, force, vibration, noise) as a function of electrical order or mechanical order.

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